[owltown]

Does the GLC300 require a battery tender for a car not driven all the time?
If true, what type and size its needed?

 

[CRNCYX]

All vehicles require it any time you have it sitting for a long time.

While you can do the math and figure out what sort of amps it needs on a consistent basis most of the popular trickle chargers charge at a rate which is safe for all batteries. So you can either go that "universal" route or check with MB to see what they recommend and can supply you with.

 

[Klass]

When you say not driven all the time, how long is it left sitting, and when you drive it, how long is it operating for?

 

[maldoman]

I bought Deltran Battery Tender 4.5 amp, 1.25 amp also good but longer to charge. My AMG driven on weekend, my SLK driven weekdays but only 60 miles for the week.

This is a battery maintainer that's keeps the battery at its best without over charging for months if need be, both cars always get the Tender treatment!